The present invention relates to a trailing edge air cooling configuration for a turbine nozzle, and particularly relates to a hybrid convective channel and pin cooling configuration for the trailing edge portion of a gas turbine nozzle vane.
Gas turbine nozzle cooling is typically achieved by locating impingement inserts within the airfoil cavities, e.g., two or more cavities of the first stage nozzle of a gas turbine. The pressure and suction sides of the vane are thus impingement cooled. The post-impingement cooling air is then either discharged through film holes along the airfoil surface to provide an insulating barrier of cooler air between the hot gas stream and the airfoil or sent to an additional circuit to convectively cool the airfoil trailing edge. The additional trailing edge circuit is required due to geometric limitations of the vane, i.e., there is insufficient space within the airfoil cavity to extend the aft impingement insert to the trailing edge. Furthermore, three-dimensional advanced airfoil nozzle vanes have a high degree of bowing and twist. This lengthens the trailing edge region where impingement cooling using inserts is not mechanically practical.
Various trailing edge air cooling circuits have been proposed and utilized in the past. Certain circuits use pins extending between the opposite sides of the airfoil for receiving the post-impingement cooling flow for cooling the trailing edge portion. Pin cooling, however, is associated with a substantial pressure drop and is practical over very short distances. Turbulative convective channel designs have also been employed, resulting in a lower pressure drop. However, those designs often achieve insufficient cooling efficiency to meet cooling performance requirements for the nozzle vane. There are also examples of pin cooling and convective channel cooling circuits coexisting in the same design. However, there has developed a need for even further cooling efficiencies, particularly for nozzle vanes having a high degree of bowing and twist in enhanced three-dimensional aerodynamic designs which will meet the cooling requirements for these advanced aerodynamic designs.